The present invention relates to a toner supply device for a copier or similar image forming apparatus and, more particularly, to a toner supply device advantageously applicable to a full color copier.
It is common practice with an image forming apparatus, especially a full color copier, to arrange a plurality of developing units for implementing development in yellow, magenta, cyan and black densely around a photoconductive element. To miniaturize the individual developing units, a toner supply device may be located outside of the developing units to replenish toners as needed, as proposed in the past.
A toner supply device of the type described is disclosed in Japanese Patent Laid-Open Publication No. 178625/1988, for example. Specifically, such a toner supply device is applicable to a copier having a plurality of developing units which are rotatably mounted on a hollow support shaft and movable toward a photoconductive element one at a time in a predetermined position. The toner supply device has a plurality of external hoppers and tubes each communicating respective one of the hoppers to the interior of the hollow support shaft. Toners of different colors each is fed from one of the hoppers to the hollow support shaft by the associated tube. The toner reached the interior of the hollow shaft is supplied to a particular developing unit via a hole which is formed through the wall of the shaft. To increase the space for accommodating the toners of different colors, the hoppers have special shapes and are combined together such that their toner inlet ports are positioned in an array in the front-and-rear or longitudinal direction of the copier body. Further, the hoppers are located at one side and in an upper portion of the copier body and is bodily enclosed by a cover.
Japanese Patent Laid-Open Publication 166565/1986 teaches a toner supply device having a hopper which is rotatable in a toner supply section. To replenish the hopper, the hopper is rotated toward the outside of an apparatus so that a toner supply port thereof may be accessible from the outside. Specifically, an upper portion of the hopper is so tiled as to position the toner inlet port of the hopper in a substantially horizontal position.
The conventional toner supply device of the type using a plurality of external hoppers has various problems left unsolved, as follows. Since the toner inlet ports of the hoppers are sequentially arranged in the longitudinal direction of the apparatus body, attaching toner cartridges to the hoppers located at the rear side is troublesome. Moreover, when toners of different kinds should be supplied at the same time, the cartridges at the front side obstruct the operator's manipulations when it comes to the hoppers located at the rear side, and the operator is apt to mount a wrong toner cartridge. Regarding a full color copier using many different kinds of toners, this not only lowers the efficiency of copying work but also causes toners of different colors to be mixed together. Furthermore, the developing units and their associated external hoppers are communicated by individual tubes, and the hoppers are bodily enclosed by a cover, as stated earlier. Hence, to inspect or repair one supply unit, all the supply units have to be removed from the copier body to disassemble, among others, the connecting portions of the tubes and to connect the individual tubes again to the interior of the hollow support shaft. This shaft in difficult maintenance and disassembly.
On the other hand, the problem with the rotatable hopper scheme is that the volume of the hopper is limited since the upper portion thereof has to be tilted to bring the toner inlet port to a substantially horizontal position. Moreover, to minimize the decrease in volume, the toner supply port has to be positioned close to the apparatus body. As a result, it is likely that the toner is scattered around during the toner supply to contaminate the apparatus.